The present invention relates generally to determining the dynamic state of an automotive vehicle, and more particularly, to a method and apparatus for determining lateral velocity of an automotive vehicle.
It is a well-known practice to control various operating dynamics of a motor vehicle to achieve active safety, using yaw and roll stability control systems. The effective operation of the various safety control devices requires high-accuracy and fast-response-time of the operating state of the motor vehicle, regarding the various road conditions and driving conditions. One important operating state used in such systems is the vehicle lateral velocity.
As a vehicle is driven, it may slide with respect to the road surface along the vehicle lateral axis, especially when it is driven on a low friction (low mu) road surface. This sliding can be quantitatively estimated using the lateral velocity of the center of gravity of the vehicle, projected on the lateral direction of the vehicle. The lateral velocity combined with other vehicle dynamic variables, such as longitudinal velocity and yaw rate, may be used for vehicle attitude sensing. The vehicle attitude may be used to generate control commands for vehicle yaw and roll stability control systems. Lateral velocity may be directly measured by sensors such as optical sensors or global positioning system (GPS) sensors. However, those sensors are very costly for the current vehicle dynamics controls. Hence it is desirable to use other available sensor signals to estimate the vehicle lateral velocity.
Many known systems rely upon basic assumptions regarding conditions such as driving on a flat surface (no pitch or bank angle), or on a high mu surface, or with a small vehicle attitude change. One example of such a system is found in U.S. Pat. No. 5,742,919, which provides a method to estimate the lateral velocity. The disclosed method is accurate only when the road is flat, the road surface has high mu, and vehicle has very small roll motion.
Another known method uses a lateral acceleration sensor signal to construct the time derivative of the vehicle lateral velocity by taking away the product of the yaw rate and the vehicle longitudinal velocity. Since the road condition (for example, the road bank and slope), the dynamic roll, and the dynamic pitch attitude of the vehicle will generate an extra component in the lateral acceleration, this method fails to detect accurate lateral velocity on banked/slope road or when the vehicle body has significant attitude changes. For example, an aggressive driver steering input may cause large roll attitude variation of the vehicle; during off-road driving, the large road bank and slope will be experienced through vehicle attitude changes. A vehicle with large lateral acceleration maneuvers could achieve 6 degrees of relative roll angle between the vehicle body and a level road surface. If such a vehicle is driven at 45 mph off camber on a 10 degree banked road, the lateral acceleration sensor reading will be increased by 2.7 m/s2 solely due to gravity. Hence, neglecting the road bank and the vehicle roll information could introduce an error of 2.7 m/s per second. That is, a 2 second maneuver in this case will end up with around 5.4 m/s lateral velocity error which is more than 27% of the vehicle speed of 45 mph.
It would therefore be desirable to provide a robust determination of lateral velocity that is reliable on roads having banks, slopes, various surface mu""s and when the vehicle is operating under changing dynamic conditions.
The present invention provides a robust determination of lateral velocity of the vehicle that maintains high accuracy by incorporating or compensating for various dynamic conditions of the vehicle and for various road conditions.
In one aspect of the invention, an apparatus for determining lateral velocity of an automotive vehicle includes a vehicle speed sensor that generates a vehicle speed signal, a roll rate sensor for generating a roll rate signal, a yaw rate sensor for generating a yaw rate signal, a lateral acceleration sensor for generating a lateral acceleration signal, and a longitudinal acceleration sensor for generating a longitudinal acceleration signal. A controller is coupled to the sensors and determines a steady state pitch angle and a steady state roll angle as a function of the lateral acceleration signal, the longitudinal acceleration signal, the yaw rate signal, and the vehicle speed signal. The controller determines a sliding index as a function of the steady state pitch signal, the steady state roll angle, and the roll rate signal. The controller determines lateral velocity as a function of the sliding index.
In a further aspect of the invention, a method of controlling a vehicle comprises measuring a vehicle speed; measuring a roll rate of the vehicle; measuring a yaw rate signal of the vehicle; measuring a lateral acceleration signal of the vehicle; measuring a longitudinal acceleration of the vehicle; and determining a lateral velocity as a function of the longitudinal acceleration, the vehicle speed, the lateral acceleration signal, the yaw rate signal and the roll rate signal; and controlling a safety system in response to the lateral velocity and the other calculated and measured variables.
It is an advantage of the present invention that a closed form formula for lateral velocity and a reliable computation provides an estimation of the vehicle lateral velocity. It is a further advantage of the present invention that the estimation of the lateral velocity is accurate regardless of road profile (flat, banked, or graded road surface), road surface condition (low or high mu), and driving conditions (large or small roll/pitch/yaw combined motion).
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.